Expansion of human hematopoietic progenitor cells in a liquid medium

ABSTRACT

A process for supporting hematopoietic progenitor cells in a culture medium which contains at least one cytokine effective for supporting the cells, and preferably, is essentially free of stromal cells.

This application is a continuation-in-part of U.S. Ser. No. 07/682,344, filed Apr. 9, 1991, now abandoned.

This invention relates to a system and process for supporting human stem cells and more particularly the present invention relates to supporting hematopoietic stem cells for use in bone marrow transplant patients.

Mammalian hematopoiesis has been studied in vitro through the use of various long-term marrow culture systems (3, 10-12). Dezter and co-workers (3) described a murine system from which CFU-S an CFU-GM could be assayed for several months, with erythroid and megakaryocytic precursors appearing for a more limited time. Maintenance of these cultures was dependent on the formation of an adherent stromal cell layer composed of endothelial cells, adipocytes, reticular cells, an macrophages. These methods were soon adapted for the study of human bone marrow. Human long-term culture systems were reported to generate assayable hematopoietic progenitor cells for 8 or 9 weeks (10, 11) and, later, for up to 20 weeks (12, 13). Such cultures are again relying on the pre-establishment of a stromal cell layer which is frequently reinoculated with a large, heterogeneous population of marrow cells. Hematopoietic stem cells have been shown to home and adhere to this adherent cell multilayer before generating and releasing more committed progenitor cells (1, 14, 15). Stromal cells are thought to provide not only a physical matrix on which stem cells reside, but also to produce membrane-contact signals and/or hematopoietic growth factors necessary for stem cell proliferation and differentiation (4, 5, 16, 17). This heterogeneous mixture of cells comprising the adherent cell layer presents an inherently complex system from which the isolation of discrete variables affecting stem cell growth has proven difficult.

Recently, a study was conducted by McNiece and Langley which examined the stimulatory effect of recombinant human stem cell factor (MGF) on human bone marrow cells alone and in combination with recombinant human colony stimulating factors, GM-CSF, IL-3 and erythropoietin. The results showed that MGF stimulation of low density non-adherent, antibody depleted CD34⁺ cells suggests that MGF directly stimulates progenitor cells capable of myeloid and erythroid differentiation (18).

In accordance with an aspect of the present invention there is provided a process for supporting mammalian bone marrow cells wherein such cells are maintained in a culture medium essentially free of stromal cells and which includes at least one cytokine effective for supporting such cells.

Preferred embodiments of this aspect of the present invention provide a process for supporting bone marrow cells which are hematopoietic stem cells, a process for supporting bone marrow cells which are hematopoietic progenitor cells and a process for supporting bone marrow cells which are CD34⁺ DR⁻ CD15⁻ cells.

In addition, this invention provides that at least one cytokine be selected from the following cytokines: Interleukin (IL)-1, IL-3, IL-6, granulocyte/macrophate-colony stimulating factor (GM-CSF), human or murine stem cell factor, sometimes referred to as human or murine mast cell growth factor (MGF) and a fusion protein of GM-CSF/IL-3 (FP). Further, this invention provides particularly preferred embodiments wherein the cytokine MGF is included as the sole cytokine or in combination with at least one other cytokine.

In accordance with another aspect of the present invention there is provided a process for supporting mammalian bone marrow cells wherein such cells are maintained in a culture medium containing a combination of cytokines effective for supporting such cells. Preferably, the bone marrow will be supported in a culture medium which is essentially free of stromal cells.

Another aspect of the present invention provides for a process of supporting mammalian bone marrow cells wherein such cells are maintained in a culture medium which is essentially free of serum and of stromal cells. This system allows for preferred expansion of progenitor cell numbers and enables the identification of which cytokines specifically affect progenitor cell expansion.

Another aspect of the present invention provides for a process of supporting mammalian bone marrow cells wherein such cells are maintained in a culture system which is essentially a serum-free long-term suspension human bone marrow. This system allows for preferred expansion of human progenitor cell numbers and enables the identification of which cytokines specifically affect human progenitor cell expansion. Preferably, the medium is essentially free of stromal cells.

Additional preferred embodiments of this invention provide a process for supporting bone marrow cells which are hematopoietic stem cells, a process for supporting bone marrow cells which are hematopoietic progenitor cells and a process for supporting bone marrow cells which are CD34⁺ DR⁻ CD15⁻ cells.

Preferably, the culture medium will contain at least one of the following cytokine combinations: IL-1/IL-3; IL-3/IL-6; IL-3/KGF; IL-3/GM-CSF; MGF/FP. Applicant has found that such combinations provide for an improved rapid expansion of the cells population.

The term "supporting" with respect to stem cells and other progenitor cells means maintaining and/or expanding and/or promoting some differentiation of such cells.

The following are representative examples of cytokines which may be employed in the present invention: IL-1 in an amount effective to support the cells. Generally, such amount is at least 20 pg/ml and need not exceed 1 ng/ml, preferably 1 ng/ml; IL-6 in an amount effective to support the cells. Generally, such amount is at least 20 pg/ml and need not exceed 1 ng/ml, preferably 1 ng/ml; IL-6 in an amount effective to support the cells. Generally, such amount is at least 1 ng/ml and need not exceed 50 ng/ml preferably 10 ng/ml; IL-3 in an amount effective to support the cells. Generally, such amount is at least 500 pg/ml and need not exceed 2 ng/ml preferably 500 pg/ml; GM-CSF in an amount effective to support the cells. Generally, such amount is at least 100 pg/ml and need not exceed 1 ng/ml, preferably 200 pg/ml; MGF in an amount effective to support the cells. Generally, such amount is at least 10 ng/ml and need not exceed 50 ng/ml, preferably 50 ng/ml; and FP in an amount effective to support the cells. Generally, such amount is at least 1 ng/ml and need not exceed 10 ng/ml, preferably 10 ng/ml. Such cytokines may be employed alone or in combination with each other.

The use of a cytokine in the absence of stromal cells is particularly suitable for expanding the mammalian bone marrow stem cells and in particular progenitor cells. The cells which are supported in accordance with the present invention are preferably of human origin.

In accordance with a preferred aspect of the present invention, a cell population which is supported in accordance with the present invention is that which is positive for CD34 antigen and is negative for HLA-DR and is also negative for CD15.

Specifically, this aspect of the present invention provides for cell population of CD34⁺ DR⁻ CD15⁻ supported in accordance with the process described above, where the population has doubled in a period of time which does not exceed 15 days. Preferably, the population has doubled in 7 to 15 days.

In accordance with another aspect, the present invention provides for a cell population of bone marrow cells supported in accordance with the process described herein, where the population has doubled in a period of time which does not exceed 15 days. Preferably, the population has doubled in 7 to 15 days.

In accordance with another aspect, the present invention provides for a cell population of hematopoietic stem cells supported in accordance with the process described herein, wherein the population has doubled in a period of time which does not exceed 15 days. Preferably, the population has doubled in 7 to 15 days.

In accordance with another aspect, the present invention provides for a cell population of hematopoietic progenitor cells supported in accordance with the process described herein, where the population has doubled in a period of time which does not exceed 15 days. Preferably,the population has doubled in 7 to 15 days.

Another aspect of the present invention provides for a composition comprised of an expanded bone marrow cell culture which is essentially free of stromal cells, the culture also contains at least one cytokine and the culture's cell population has doubled in a time not exceeding 15 days. Preferably, the cell population will have doubled in at least 7 and not exceeding 15 days.

Human long-term bone marrow cultures (LTBMC) have been though to require the formation of an adherent stromal cell layer for sustained in vitro hematopoiesis. The CD34⁺ DR⁻ CD15⁻ population of human marrow cells are capable of multilineage differentiation, self-renewal, and of initiating LTBMC in the absence of stromal cells for up to 12 weeks when continually supplied with cytokines. Preferably the cytokine supplied is interleukin-3 (IL-3). The effects of stromal cells on CD34⁺ DR⁻ CD15⁻ cells in the presence and absence of IL-3 in LTBMC have been observed. Suspension cultures of CD34⁺ DR⁻ CD15⁻ cells in the absence of stroma were characterized by sustained hematopoiesis for 10-12 weeks as demonstrated by a high degree of cellular proliferation and multilineage progenitor cell expansion when supplied with IL-3. No adherent layer formed in these cultures, and IL-3 was necessary for their survival beyond one week. Such stroma-free cultures produced 500 to more than 900 assayable CFU-GM over a 12-week period, while BFU-E were generated for 1-3 weeks. By contrast, 4-week-old stromal cultures recharged with autologous CD34⁺ DR⁻ CD15⁻ cells both in the presence and absence of exogenous IL-3 generated far fewer (100-500) assayable colony-forming cells for only six weeks, and production of nonadherent cells was greatly reduced over the 12-week observation period. Stromal cultures supplemented with IL-3 but not re-seeded with CD34⁺ DR⁻ CD15⁻ cells behaved similarly to those to which sorted cells were added. These data suggest that marrow stromal cells modulate the effects of cytokines on hematopoietic stem cell development and proliferation and elaborate signals that both promote and dampen in vitro hematopoieses.

An additional aspect of the present invention provides for a composition comprised of an expanded bone marrow cell culture which contains a combination of cytokines and the cultures cell population has doubled in a time not to exceed 15 days. Preferably the cell population has doubled in at least 7 and not exceeding 15 days. It is also preferable, that the cell culture be essentially free of stromal cells.

As previously indicated, the present invention is particularly applicable to bone marrow cells that are positive for CD34 antigen but which do no express HLA-DR, CD15 antigens in that it is believed that such cell population is believed to be closely associated with human hematopoietic stem cells, but it is to be understood that the present invention is not limited to supporting such a cell population.

The cells supported in accordance with the present invention may be used in a variety of ways. For example, such cells may be employed as part of a bone marrow transfer procedure.

Expanded hematopoietic stem cell populations can be used as grafts for marrow transplantation to treat malignancies, bone marrow failure states and cogenital metabolic, immunologic and hematological disorders. Marrow samples will be taken from patients with cancer and CD34⁺ DR⁻ CD15⁻ cells isolated by means of density centrifugation, counterflow centrifugal elutriation, monoclonal antibody labeling and fluorescence activated cell sorting. The stem cells in this cell population will then be expanded in vitro and will serve as a graft for autologous marrow transplantation. The graft will be infused after the patient has received curative chemo-radiotherapy.

Expanded stem cell populations can also be utilized for in utero transplantation during the first trimester of pregnancy. Fetuses with metabolic and hematologic disorders will be diagnosed prenatally. Marrow will be obtained from normal individuals and CD34⁺ DR⁻ CD15⁻ cells will be obtained by the methods described previously and expanded in vitro. They will then be administered to the fetus by in utero injection. A chimera will be formed which will lead to partial but clinically significant alleviation of the clinical abnormality.

The invention will be further described with respect to the following examples; however, the scope of the invention is not to be limited thereby:

EXAMPLE 1 A. Materials and Procedures

Prior to performing any procedures, informed consent was obtained from all volunteers according to the guidelines of the Human Investigation Committee of the Indiana University School of Medicine.

Cell Separation Techniques

Bone marrow aspirates were collected from the posterior iliac crests of normal volunteers Low-density mononuclear bone marrow (LDBM) cells were obtained by density centrifugation of the heparinized marrow over Ficoll-Pague (Pharmacia Fine Chemicals, Piuscataway, N.J.) at 500 g for 25 min. LDBM cells were suspended in PBS-EDTA (PBS, pH 7.4, containing 5% FBS, 0.01% EDTA wt/vol, and 1.0 g/liter D-glucose) and injected into an elutriator system at 10° C. at a rotor speed of 1,950 rpm using a JA-17 rotor and standard separation chamber (Beckman Instruments, Inc., Palo Alto, Calif.). A fraction of the LDBM eluted at a flow rate of 12-14 ml/min (FR 12-14), enriched for hematopoietic precursors, was collected as previously described (2).

Long-term Marrow Cultures Free of Stromal Cells

Plastic 35-mm tissue culture dishes were seeded with 2×10⁶ LDBM cells in 1 ml of Iscove's with 10% FBS and 2×10⁻⁵ M methylprednisolone. Cultures were incubated at 37° C. in 100% humidified atmosphere containing 5% CO₂ in air and fed weekly by total replacement of media. Stromal cells were confluent by 4-6 wk. The stromal cultures were then irradiated with 1,500 rad, the media were replaced, and the cultures were inoculated with 5×10³ sorted bone marrow cells from autologous donors. The media in these cultures were removed at 7-10 d intervals and replaced with fresh media. Suspended, nonadherent cells were then counted and assayed for progenitors.

Long-term Suspension Cultures

Plastic 35-mm tissue culture dishes containing 1 ml of Iscove's with 10% FBS were inoculated with stromal cell free long term marrow cells containing 5×10³ cells obtained by sorting and incubated at 37° C. in 100% humidified atmosphere containing 5% CO₂ in air. At this time, and every 48 h thereafter, cultures received nothing (1% BSA/PBS), 2.5 U/ml IL-1a, 50 U/ml IL-3, 75 U/ml IL-6, 12.5 U/ml GM-CSF, or combinations of the above. At 7d intervals, cultures were demi-depopulated by removal of one-half the culture volume which was replaced with fresh media. Cells in the harvested media were counted, transferred to slides for staining and morphological examination, and assayed for various progenitor cells.

Hematopoietic Growth Factors

All cytokines were obtained from the Genzyme Corp., Boston, Mass. Recombinant IL-1a and In-3 each had a specific activity of 10⁸ CFU/mg protein, while that of IL-6 was 10⁷ and granulocyte/macrophage colony-stimulating factor (GM-CSF) 5×10⁷ CFCc/mg protein.

Two- and Three-color Cell Sorting

FR 12-14 cells were incubated with mouse monoclonal anti-HPCA-1 (CD34) of the IgG₁ subclass (Becton Dickinson Immunocytometry Systems, San Jose, Calif.), washed, and stained with Texas red-conjugated, subclass-specific goat anti-mouse IgG₁ (Southern Biotechnology Associates, Inc., Birmingham, Ala.). Cells were next incubated with mouse serum to block any unbound active sites on the second-step antibody. Cells were finally stained with phycoerythrin-conjugated mouse anti-HLA-DR either alone or in combination with FITC-conjugated CD33 (My9, Coulter Immunology, Hialeah, Fla.), CD15 (Leu-M1), or CD71 (transferring receptor) (Becton Dickinson Immunocytometry Systems). CD15 is present on cells of the granulocytic and monocytic lineages, and an anti-CD15 monoclonal antibody was employed in the hope of eliminating these cellular components from the cell populations (6). CD71 is present on actively proliferating cells and an anti-CD71 antibody was utilized to separate actively proliferating cells from more quiescent marrow elements (7). Controls consisted of the corresponding isotype-matched, nonspecific myeloma proteins used in parallel with staining monoclonal antibodies. Cells were stained at a concentration of 2×10⁷ /ml and washed after each step in 1% BSA in PBS. A temperature of 4° C. was maintained throughout the procedure.

Immediately after staining, cells were sorted on a Coulter Epics 753 dual-laser flow cytometry system (Coulter Electronics, Inc., Hialeah, Fla.). Texas red was excited by 590 nm light emitted from a rhodamine 6G dye laser. FITC and phycoerythrin were excited using the 488 nm wavelength from a dedicated 6-W argon laser. Sorting windows were first established for forward angle light scatter (FALS) and Texas red fluorescence. Positivity for each fluorochrome was defined as fluorescence >99% of that of the controls. Cells were next gated on the presence or absence of detectable HLA-DR-phycoerythrin and CD33-FITC, CD15-FITC, or CD71-FITC.

Hematopoietic Progenitor Cells Assays

Cells were suspended at various concentrations in 35-mm plastic tissue culture dishes (Costar Data Packaging, Cambridge, Mass.) containing 1 ml of 30% FBS, 5×10⁻⁵ M 2-mercaptoethanol, 1 U human purified erythropoietin (50 U/mg protein, Toyobo Colo. Ltd., Osaka, Japan), 50 U GM-CSF, and 1.1% methylcellulose in Iscove's modified Dulbecco's medium. The cultures were incubated at 37° C. in a 100% humidified atmosphere containing 5% Co₂ in air. After 14 d, erthropoietic bursts (BFU-E), granulocyte-macrophage (CFU-GM), and mixed lineage (CFU-GEMM) colonies were scored in situ on an inverted microscope using standard criteria for their identification (2).

High proliferative potential colony-forming cell (HPP-CFC)-derived colonies were enumerated after 28 d in culture according to the recently published criteria of McNiece and co-workers (8). The human HPP-CFC derived colony is a late-appearing, very large (0.5 mm or more in diameter) colony composed primarily of granulocytes with a lesser number of monocytes; cell numbers frequently exceed 50,000.

Cells removed from suspension cultures were assayed for CFU-megakaryocyte (CFU-MK) colonies using the serum-depleted method described in detail by Bruno et al. (9) 5×10³ cells per point were suspended in a 1-ml serum-substituted fibrin clot with 100 U of IL-3 in 35-mm culture dishes and incubated at 37° C. in a 100% humidified atmosphere containing 5% CO₂ in air. At 18-24 d, cultures were fixed in situ and stained using rabbit anti-human platelet glycoprotein antisera, and fluorescein-conjugated goat F(ab')2-specific anti-rabbit IgG (Tago, Inc., Burlingame, Calif.) and megakaryocyte colonies were enumerated on a Zeiss fluorescence microscope (Carl Zeills, Inc., New York, N.Y.). A positive colony was defined as a cluster of three or more fluorescent cells.

B. Experiments

A liquid culture system supplemented with repeated 48-hourly cytokine additions was utilized to study cell populations. Total cell production by both CD34⁺ DR⁻ CD15⁻ and CD34⁺ DR⁻ CD71⁻ cells is shown in Tables I and II while assayable CFU-GM in these cultures over time are recorded in Tables III and IV. In the absence of exogenous cytokines, total cell numbers declined over a 2-wk period and assayable CFU-GM persisted for only 1 or 2 wk. The repeated addition of IL-1a did not significantly enhance total cell production or generation of CFU-GM by either CD34⁺ DR⁻ CD15⁻ or CD34⁺ DR⁻ CD71⁻ cells. IL-6 did not alter total cell numbers or numbers of assayable CFU-GM in cultures initiated with CD34⁺ DR⁻ CD71⁻ cells. By contrast, IL-6 increased total cell numbers over seven fold by week 3 by CD34⁺ DR⁻ CD15⁻ initiated cultures but did not appreciably extend the interval over which CFU-GM were detected. In both sets of experiments, GM-CSF promoted increased total cell production for 6 wk, by which time cell numbers represented 20-80 times the number present in the initial seeding populations. Assayable CFU-GM persisted for 3-4 wk and cumulatively surpassed those assayable in the initial populations. The single most effective cytokine in terms of promoting cellular expansion, increasing the number of CFU-GM, and lengthening the duration of time over which CFU-GM were assayable was IL-3. Both CD34⁺ DR⁻ CD15⁻ and CD34^(+DR) ⁻ CD71⁻ cells experienced 200-fold increases in cell numbers by day 28, and, after 1 or 2 wk in culture, contained equal or slightly greater numbers of CFU-GM than present in the initial inoculi. Assayable progenitors were produced for 4- 5 wk in the system when maintained with IL-3, and viable cell counts remained high at 8 wk. IL-1a or IL-6 prolonged and enhanced these effects when added in combination with IL-3. CFU-GM were assayable after 8 wk in suspension culture after continued treatment with these two cytokine combinations. No adherent cell layer was established in any of the suspension cultures over the 8 wk period of observation.

In a separate experiment, CD34⁺ DR⁻ CD71⁻ cells were grown in this suspension culture system in the presence of a combination of both IL-3 and IL-6 and assayed for CFU-MK from days 7 through 28 of culture. CFU-MK were detected over this 28 d period (Table V). Utilizing this IL-3/IL-6 cytokine combination, the ability of CD34⁺ DR⁻ CD15⁺ and CD34⁺ DR⁻ CD71⁺ cells to sustain long-term hematopoiesis was compared to that of the CD34⁺ DR⁻ CD15⁻ and CD34⁺ DR⁻ CD71⁻ fractions (Table VI). Both the CD15-positive and CD71-positive calls failed to generate CFU-GM after 2 wk, and the CD71-positive population, which initially included the overwhelming majority of BFU-E, failed to produce assayable BFU-E after only 7 d in culture.

Morphological analysis of the cells in these suspension cultures during the period of observation revealed changes in the cellular composition of the populations following the addition of various cytokines (Tables VII and VIII). IL-1a-and IL-6-containing cultures behaved very similarly to the control samples. Cultures to which no cytokines were added were composed of 90-100% blasts after 1 wk; the CD34⁺ DR⁻ CD15⁻ cells did not survive 2 wk in the absence of cytokine whereas the CD34⁺ DR⁻ CD71⁻ initiated cultures were composed of 40% blasts and 60% monocytes by week 2. Cultures receiving IL-1a had a similar cellular composition. IL-6 facilitated some differentiation to the granulocytic series by both cell populations; the CD34⁺ DR⁻ CD15⁻ cells produced a significant number of mature granulocytic elements by week 2. GM-CSF, as well as IL-3, reduced the percentage of blasts in these suspension cultures appreciably by day 7. GM-CSF-containing cultures of CD34⁺ DR⁻ CD15⁻ cells consisted primarily of metamyelocytes through 4 wk, with a shift to monosytes occurring by week 6.

IL-3 was unique in that, at 3 wk, suspension cultures initiated by either CD34⁺ DR⁻ CD15⁻ or CD34⁺ DR⁻ CD71⁻ cells were composed of 48% basophils in the presence of this growth factor (Tables VII and VIII). Addition of IL-1a or IL-6 did not alter this trend, all IL-3-containing cultures being composed of about 50% basophils by 3 wk and retaining significant numbers of basophils throughout the duration of culture.

The cellular composition of hematopoietic colonies assayed from aliquots of the suspension cultures was comparable to those assayed from the original sorted populations with a few notable exceptions. Blast cell colonies, as well as HPP-CFC-derived colonies, were routinely obtained by directly assaying CD34⁺ DR⁻ CD15⁻ or CD34⁺ DR⁻ CD71⁻ cells while these colony types were not observed in subsequent clonal assays of cellular aliquots obtained from the long-term liquid cultures. Distribution of GM colony subtypes, however, remained fairly consistent with roughly 40% being granulocyte/macrophage, 40% monocyte/macrophage, and 20% basophil or eosinophil colonies in either assays initiated with sorted cells of those initiated on days 7 through 42 of liquid culture. These CFU-GM-derived colonies ranged in size from 100 to 2,000 cells with the average colony containing between 200 tp 400 cells. After 8 wk of suspension culture, monosyte/macrophage colonies were the predominant colony type observed in the clonal assays.

                  TABLE I                                                          ______________________________________                                         Total Cell production of CD34.sup.+, DR.sup.-, CD15.sup.-                      Cells after Addition of Various Cytokines                                             Day                                                                            0    7      14     21   28   35   42   56                               Cytokine viable cell count × 10.sup.3                                    ______________________________________                                         None     5      1      4    0    0    0    0    0                              Il-1     5      2      2    0    0    0    0    0                              IL-3.sup.+                                                                              5      53     140  591  1,085                                                                               533  678  781                            IL-6§                                                                              5      3      4    36   26   16   0    0                              GM-CSF°                                                                          5      8      14   44   169  213  118  0                              IL-1a/IL-3                                                                              5      32     167  556  1,360                                                                               1,387                                                                               758  1,069                          IL-6/IL-3                                                                               5      47     171  471  854  1,440                                                                               1,200                                                                               1,216                          ______________________________________                                          Total cells = cells/ml culture (1/2).sup.n, where n = number of previous       demidepopulations.                                                             *2.5 U/ml recombinant human IL1a were added every 48 h; specific activity      10.sup.8 CFU/mg protein.                                                       .sup.+ 50 U/ml recombinant human IL3 were added every 48 h; specific           activity 10.sup.8 CFU/mg protein.                                              §75 U/ml recombinant human IL6 were added every 48 h; specific            activity 10.sup.7 CFU/mg protein.                                              °12.5 U/ml recombinant human GMCSF were added every 48 h; specific      activity 5 × 10.sup.7 CFU/mg protein.                              

                  TABLE II                                                         ______________________________________                                         Total Cell Production of CD34.sup.+, DR.sup.-. CD71.sup.-                      Cells after Addition of Various Cytokines                                             Day                                                                            0    7      14     21   28   35   42   56                               Cytokine viable cell count × 10.sup.3                                    ______________________________________                                         None     5      1      2    0    0    0    0    0                              IL-1*    5      3      0    0    0    0    0    0                              IL-3.sup.+                                                                              5      40     226  964  746  1,190                                                                               1,120                                                                               851                            IL-6§                                                                              5      1      2    0    0    0    0    0                              GM-CSF°                                                                          5      3      34   44   45   445  438  0                              IL-1a/IL-3                                                                              5      23     202  684  1,112                                                                               835  800  1,067                          ______________________________________                                          Total cells = cells/ml culture (1/2).sup.n, where n = number of previous       demidepopulations.                                                             *2.5 U/ml recombinant human IL1a were added every 48 h; specific activity      10.sup.8 CFU/mg protein.                                                       .sup.+ 50 U/ml recombinant human IL3 were added every 48 h; specific           activity 10.sup.8 CFU/mg protein.                                              §75 U/ml recombinant human IL6 were added every 48 h; specific            activity 10.sup.7 CFU/mg protein.                                              °12.5 U/ml recombinant human GMCSF were added every 48 h; specific      activity 5 × 10.sup.7 CFU/mg protein.                              

                  TABLE III                                                        ______________________________________                                         Total CFU-GM Production by CD34.sup.+, DR.sup.-, CD15.sup.-                    Cells after Addition of Various Cytokines                                      Week                                                                           1           2      3       4    5     6    7                                   Cytokine                                                                               CFU-GM/ml culture                                                      ______________________________________                                         None    40      0      0     0    0     0    0                                 IL-1*   22      14     0     0    0     0    0                                 IL-3.sup.+                                                                             432     696    591   325  0     0    0                                 IL-6§                                                                             42      242    96    0    0     0    0                                 GM-CSF°                                                                         273     200    219   0    0     0    0                                 IL-1a/IL-3                                                                             254     397    444   408  139   152  64                                IL-6/IL-3                                                                              98      342    236   768  864   1,080                                                                               384                               ______________________________________                                          Total CFUGM = CFUGM/ml culture (1.2).sup.n, where n = number of previous       demipopulations.                                                               Cells were seeded at 5 × 10.sup.3 /ml. CFUGM in initial (day 0)          population = 555/5 × 10.sup.3 cells. Colonies grown in                   bethylcellulose containing 50 U/ml GMCSF and enumerated after 14 d.            *2.5 U/ml recombinant human IL1α were added every 48 h; specific         activity 10.sup.8 CFU/mg protein.                                              .sup.+ 50 U/ml recombinant human IL3 were added every 48 h; specific           activity 10.sup.8 CFU/mg protein.                                              §75 U/ml recombinant human IL6 were added every 48 h; specific            activity 10.sup.7 CFU/mg protein.                                              °12.5 U/ml recombinant human GMCSF were added every 48 h; specific      activity 5 × 10.sup.7 CFU/mg protein.                              

                  TABLE IV                                                         ______________________________________                                         Total CFU-GM Production by CD34.sup.+, DR.sup.-, CD71.sup.-                    Cells after Addition of Various Cytokines                                      Week                                                                           1           2      3       4    5     6    8                                   Cytokine                                                                               CFU-GM/ml culture                                                      ______________________________________                                         None    15      4      0     0    0     0    0                                 IL-1*   20      0      0     0    0     0    0                                 IL-3.sup.+                                                                             664     272    96    448  119   0    0                                 IL-6§                                                                             51      14     0     0    0     0    0                                 GM-CSF°                                                                         402     360    135   28   0     0    0                                 IL-1/IL-3                                                                              347     324    342   334  167   240  214                               ______________________________________                                          Total CFUGM = CFUGM/ml culture (1/2).sup.n, where n = number of previous       demipopulations.                                                               Cells were seeded at 5 × 10.sup.3 /ml. CFUGM in initial (day 0)          population = 690/5 × 10.sup.3 cells. Colonies grown in                   methylcellulose containing 50 U/ml GMCSF and enumerated after 14 d.            *2.5 U/ml recombinant human IL1a were added every 48 h; specific activity      10.sup.8 CFU/mg protein.                                                       .sup.+ 50 U/ml recombinant human IL3 were added every 48 h; specific           activity 10.sup.8 CFU/mg protein.                                              §75 U/ml recombinant human IL6 were added ever 48 h; specific             activity 10.sup.7 CFU/mg protein.                                              °12.5 U/ml recombinant human GMCSF were added every 48 h; specific      activity 5 × 10.sup.7 CFU/mg protein.                              

                  TABLE V                                                          ______________________________________                                         Assayable CFU-MK in Long-Term Suspension Cultures                              of CD34.sup.+  DR.sup.- CD71.sup.-  Cells Receiving                            a Combination of Il-3 and IL-6                                                 Days in culture*                                                                             CFU-MK/ml culture.sup.+                                          ______________________________________                                          7            42.6 ± 7.6§                                              14            67.6 ± 56.6                                                   21            17.0 ± 11.8                                                   28            20.2 ± 10.4                                                   ______________________________________                                          50 U/ml recombinant human IL3 were added every 48 h; specific activity         10.sup.8 CFUc/mg protein. 75 U.ml recombinant human IL6 were added every       48 h; specific activity 10.sup.7 CFU/mg protein.                               *Cultures were demidepopulated every 7 d.                                      .sup.+ CFUMK were assayed in serumfree fibrin clot culture containing 100      U/ml IL3 colonies enumerated at days 18-24 of culture.                         §Each point represents the mean ± SD of triplicate assays.             Values are not corrected for the effects of demidepopulated.             

                  TABLE VI                                                         ______________________________________                                         Total CFU/GM and BFU-E Production by Sorted Cell                               Populations Stimulated with a Combination of IL-3 and IL-6                                Week                                                                           1     2        3      4    6   8                                    Population   CFU-GM (BFU-E) ml cultures                                        ______________________________________                                         CD34.sup.+ DR.sup.- CD15.sup.-                                                              275(10) 286(4)   64   32   75  0                                  CD34.sup.+ DR.sup.- CD15.sup.+                                                              7(1)    26       0    0    0   0                                  CD34.sup.+ DR.sup.- CD71.sup.-                                                              220(5)  330(4)   132  18   43  0                                  CD34.sup.+ DR.sup.- CD71.sup.+                                                              13      16       0    0    0   0                                  ______________________________________                                          Total CFU = CFU/ml culture/(1/2).sup.n = number of previous                    demidepopulations. 50 U/ml recombinant human IL3, specific activity            10.sup.8 CFU/mg protein and 75 U.ml recombinant human IL6, specific            activity 10.sup.7 CFU/mg protein were added every 48 h. Cells were seeded      at 5 × 10.sup.3 /ml.                                               

                                      TABLE VII                                    __________________________________________________________________________     Differential Analysis of CD34.sup.+, DR.sup.-, CD15.sup.-                      Cells after Addition of Various Cytokines                                                                   Band                                              Cytokines                                                                             Day Blasts                                                                              Pro Myelo                                                                               MM  %   Seg Eo Baso                                                                               E  Mo                              __________________________________________________________________________     Control                                                                               7   100                                                                 IL-1α*                                                                          7   100                                                                        14  78                                  22                              IL-6.sup.+                                                                            7   100                                                                        14  27   11       9       13     38     2                                      21  9             48  2   7      17     17                                     28                30      4             66                              GM-CSF§                                                                          7   25   24       27  3   21                                                   14  9    1        46  3   21     13     7                                      21  3    2   1    62  3   5      22     2                                      28  6        1    43  7   3      6   2  32                                     35           4                          96                                     42           1                          99                              IL-3°                                                                          7   21   44       35             1                                             14  7    7        53             33                                            21  8             44             48                                            28  5             35  3   9      35     13                                     35  2             16  5   20     25     32                                     42                15      2      20     63                              IL-1α/IL-3                                                                      7   1    5   1    53  12  14     14                                            14  5             34  9          52                                            21  1             53  4   3      31     8                                      28  1             42  12  5      32     8                                      35                20             27     53                                     42                8              8      84                                     56                               11     89                              IL-6/IL-3                                                                             7   19   26  2    40  5   4      4                                             14  2    2        46  3   1      46                                            21  5    1        37  1   7      48     1                                      28  4    1        37  10  8      35     5                                      42  1             8       1      9      81                                     56                2              3      95                              __________________________________________________________________________

Differential cell counts were performed on Wright-Giesma stained cytocentrifuge preparations of cells removed from liquid culture. 200 cells per sample were classified; if <200 cells appeared on a slide, all were classified. Abbreviations: Pro, promyelocytes; Myelo, myelocytes; MM, metamyelocytes; Band, neutrophil band form; Seg, segmented neutrophils; Eo, eosinophils; Baso, basophils; E, erythrocytes; and Mo, monocytes. *2.5 U/ml recombinant human IL-1a were added every 48 h; specific activity 10⁸ CFU/mg protein. +50 U/ml recombinant human IL-3 were added every 48 h; specific activity 10⁸ CFU/mg protein. §75 U/ml recombinant human IL-6 were added every 48 h; specific activity 10⁷ CFU/mg protein. °12.5 U/ml recombinant human GM-CSF were added every 48 h; specific activity 5×10⁷ CFU/mg protein.

                                      TABLE VIII                                   __________________________________________________________________________     Differential Analysis of CD34.sup.+, DR.sup.-, CD71.sup.-                      Cells after Addition of Varios Cytokines                                                                    Band                                              Cytokines                                                                             Day Blasts                                                                              Pro Myelo                                                                               MM  %   Seg Eo Baso                                                                               E  Mo                              __________________________________________________________________________     Control                                                                               7   90                                  10                                     14  40                                  60                              IL-1α*                                                                          7   82                                  18                              IL-6.sup.+                                                                            7   43   4                              13                                     14  33   20                             47                              GM-CSF§                                                                          7   39   33       9   5   6      5      2                                      14  18   5        42  3   12     20                                            21  4        1    66  9   7             4                                      28  2             61  3   1   8         24                                     35  14            18  8   8   9         52                                     42                                      100                             IL-3°                                                                          7   52   40       1   2   2      2   1                                         14  29   26       26  2   3      14                                            21  13   4   2    28  2   3      48                                            28  14   3        35  5   1      35     7                                      35  9             20  7   6      27     31                                     42  2             5       4      16  2  71                              IL-1α/IL-3                                                                          7    48  42       6   2   1      2                                         14  4    1   53   4   5       33                                               21  3             44  1   1      49     2                                      28  21   3        34  4   3   1  27     8                                      35  3             23  4   29     20     21                                     42  1             7   3   3      16     70                                     56                        1      8      91                              __________________________________________________________________________

Differential cell counts were performed on Wright-Giesma stained cytocentrifuge preparations of cells removed from liquid culture. 200 cells per sample were classified; if <200 cells appeared on a slide, all were classified. Abbreviations as in Table VII. *2.5 U/ml recombinant human IL-1a were added every 48 h; specific activity 10⁸ CFU/mg protein. +50 U/ml recombinant human IL-3 were added every 48 h; specific activity 10⁸ CFU/mg protein. §75 U/ml recombinant human IL-6 were added every 48 h; specific activity 10⁷ CFU/mg protein. °12.5 U/ml recombinant human GM-CFS were added every 48 h; specific activity 5×10⁷ CFU/mg protein.

EXAMPLE 2

Long-term bone marrow cultures (LTBMC) were initiated with 5×10³ CD34⁺ DR⁻ CD15⁻ marrow cells/ml in the absence of an adherent cell layer to which murine mast cell growth factor (MGF) alone or in combination with IL-3 or a GM-CSF/IL-3 fusion protein (FP: Williams et al. Exp. Hematol. 18: 615, 1990) were added every 48 hours. In cultures not receiving cytokines, viable cells were not detectable after two weeks while cultures receiving IL-3, FP, or MGF sustained hemotopoiesis for 10 weeks. Addition of IL-3 or FP alone increased cell numbers by 10³ fold by day 56, while the combination of MGF and FP expanded cell numbers 10⁵ -fold (5×10³ cells at day 0; 5.5×10³ at day 56). Over the 10 week period of LTBMC, treatment with various cytokines led to the following cumulative increases over an input of 213 total assayable hematopoietic progenitor cells (HPC; CFU-GM+BFU-E+CFU-MK): IL-3, 868 : FP, 1,265; MGF, 2,006 MGF+IL-3, 4,845; MGF+FP, 155,442. LTBMCs receiving MGF alone possessed a higher HPC cloning efficiency than those receiving IL-3 or FP and its addition increased the cloning efficiencies of cultures containing of IL-3 and FP. The presence of MGF did not increase the longevity of cultures receiving these cytokines.

                  TABLE IX                                                         ______________________________________                                         Total Cell Production of CD34.sup.+, DR.sup.-, CD15.sup.-  Cells after         Addition of Various Cytokines                                                                 Day                                                                            0          26                                                                    Viable Cell                                                   Cytokine         count × 10.sup.3                                        ______________________________________                                         None             5            0                                                *IL-3            5            140      100%                                    .sup.+ GM-CSF    5            100                                              °FP       5            1,400                                            MGF              5            520                                              GM-CSF/IL-3      5            560                                              MGF/GM-CSF       5            12,500    20%                                    MGF/IL-3         5            1,200                                            MGF/FP           5            10,000                                           ______________________________________                                          Total cells/ml culture/1/2Yn = number of previous cell dilutions.              Cultures were periodically split to allow for cellular expension and to        perform several analyses at different time points.                             *500 pg/ml recombinant human IL3 was added every 48 hours                      .sup.+ 200.0 pg/ml recombinant human GMCSF was added every 48 hours            °10.0 ng/ml of recombinant GMCSF-IL-3 fusion protein was added eac      day                                                                            100.0 ng/ml of murine recombinant stem cell factor (SCGF) was added every      48 hours                                                                 

                                      TABLE X                                      __________________________________________________________________________     Differential Analysis of CD34.sup.+, DR.sup.-, CD15.sup.-  Cells After         Addition of Various Cytokines on Day 26 of Suspension Culture                  Cytokines Blasts                                                                              Pro Myelo                                                                               MM  Band                                                                               Seg Lymph                                                                               Eo Baso                                                                               Mo  Norm                       __________________________________________________________________________     FP        3    7   9    9   27  3   5    2  9   0   5                          GM-CSF/IL-3                                                                              1    7   4    13  24  32  4    3  4   0   0                          MGF       32   4   9    9   13  12  7    1  1   12  0                          MGF/GM-CSF                                                                               21   10  15   12  14  7   5    2  3   11  0                          MGF/IL-3  38   3   15   12  13  4   2    2  4   7   2                          MGF/FP    37   17  16   9   9   5   1    0  6   0   5                          __________________________________________________________________________

Differential cell counts were performed on Wright Giemsa stained cytocentrifuge preparations of cells removed from liquid culture. 200 cells per sample. Abbreviation used, Norm, normoblasts, other abbreviations as in Table VII. Cytokines were added at same dose as detailed in legend of Table I.

Numerous modifications and variations of the present invention are possible in light of the above teachings; therefore, within the scope of the appended claims the invention may be practiced otherwise than as particularly described.

EXAMPLE 3

Liquid-culture systems supplemented with repeated 48 hourly cytokine additions was utilized to study cell populations cultured from two donors. Total cell production of CD34⁺ DR⁻ CD15⁻ cells is shown in Table XI while assayable CFU-GM in these cultures over time is recorded in Table XIII. In the absence of exogenous cytokines, total cell numbers declined over a 1 to 2-wk period and assayable CFU-GM persisted for only a 1 to 2-wk period. In donor 1, MGF/FP cytokine combination promoted increased total cell production for 8 wk, by which time cell numbers represented over 110×103 times the number present in the initial seeding populations. In donor 2 the same cytokine combination promoted increased total cell production for 6 wk, by which time the cell numbers represented by over 16×103 times the number present in the initial seeding population. Assayable CFU-GM for donor 1 and donor 2 cultured with MGF/FP cytokine combination persisted for 6-8 wk and 3-4 wk, respectively and significantly surpassed the CFU-GM population initially assayable.

The cytokine combination MGF/IL-3 promoted over 2×10³ fold increase in total cell production over the initial seeding for donor 1 at 6 wk and donor 2 at 8 wk. Additionally, viable cell counts remain high through 10 wk. The assayable expansion of CFU-GM for donor 1 and 2 cultured with MGF/IL-3 cytokine combination persisted for 6-8 wk for each donor and each significantly surpassed the CFU-GM population assayable initially.

Total BFU-E production by CD34⁺ DR⁻ CD15⁻ cells is shown in Table XIV. In donor 1 and donor 2 the cytokine combination MGF/FP persisted for 1-2 wk and 3-4 wk, respectively with only donor 2 showing a significant increase over the BFU-E population initially assayable. The cytokine combination MGF/IL-3 persisted in Donor 1 for 2-3 wk and in donor 2 for 3-4 wk, with both showing significant increase in wk 1-2 over the BFU-E population initially assayable. Total CFU-MK production by CD34⁺ DR⁻ CD15⁻ cells is shown in Table XV. The cytokine combination of MGF/IL-3 for both donor 1 and 2 show CFU-MK persistance for through 10 wk and each has significantly surpassed the initially assayable CFU-MK population. Donors 1 and 2 show CFU-MK persistance for 6-8 wk and 8-10 wk, respectively, both showing significant increases over the initial CFU-MK population.

Morphological analysis of the cells in the suspension cultures of donor 1 during the period of observation revealed changes in the cellular composition of the population following the addition of various cytokines, see Table XII, which shows the differential analysis of CD34⁺ DR⁻ CD15⁻ cells. Cultures receiving MGF/FP were composed of 11% blasts by 14 days and cultures receiving MGF/IL-3 were composed of 17% blasts by 14 days. The highest percentage of blasts by 14 days was in the cultures receiving MGF alone which were composed of 30% blasts. In contrast IL-3 and FP containing cultures had reduced the percentage of blasts cells appreciably by day 14.

Table XVI depicts the percentage of total cells which give rise to progenitor cells of colony forming units. Although MGF percentages are high the overall expansion of cultures receiving MGF is not as substantial, however the cultures receiving MGF/IL-3 cytokines provide high plating percentages and substantial overall expansion (see Tables XI-XV)

                  TABLE XI                                                         ______________________________________                                         Total Cell Production of CD34.sup.+, DR.sup.-, CD15.sup.-                      Cells Cultured in the Absence of Various Cytokines                             Viable cell count × 10.sup.3 /ml                                         Week                                                                           Cytokine                                                                              1      2      3     4     6     8     10                                ______________________________________                                         Donor 1                                                                        None   1      0      0     0     0     0     0                                 IL-3.sup.1                                                                            28     144    271   560   480   762   960                               GM-    12     107    436   1,085 2,680 2,080 1,760                             CSF.sup.2                                                                      IL-3/  23     244    742   1,620 1,979 2,035 2,720                             GM-CSF                                                                         FP.sup.3                                                                              42     262    587   1,240 3,000 1,494 480                               MGF.sup.4                                                                             8      104    933   N.D..sup.5                                                                           1,680 1,760 640                               MGF/   101    1,211  35,100                                                                               101,000                                                                              262,400                                                                              550,000                                                                              100,000                           FP                                                                             MGF/   38     213    978   2,820 10,800                                                                               3,680 5,120                             IL-3                                                                           Donor 2                                                                        None   1      0      0     0     0     0     0                                 IL-3   24     180    650   605   1,400 960   864                               FP     41     810    2,100 6,680 1,840 4,320 5,280                             MGF    8      27     71    98    230   70    0                                 MGF/   100    1,280  15,700                                                                               6,400 81,000                                                                               19,520                                                                               0                                 FP                                                                             MGF/   36     305    780   1,380 6,960 10,400                                                                               5,440                             IL-3                                                                           Donor 3                                                                        MGF/   N.D.   5,040  14,400                                                                               14,800                                                                               8,960                                         FP                                                                             ______________________________________                                          Total cells = cells/ml culture/(n).sup.n where n = number of                   demidepopulations.                                                             Cultures were seeded at 5 × 10.sup.3 cells/ml.                           .sup.1 500 pg/ml recombinant human IL3 was added every 48 hours; specific      activity 3.5 × 10.sup.8 CFU/mg protein                                   .sup.2 250 pg/ml recombinant human GMCSF was added every 48 hours;             specific activity 2 × 10.sup.8 CFU/mg protein.                           .sup.3 10 ng/ml recombinant human FP was added every 48 hours; specific        activity 1-2 × 10.sup.8 CFU/mg                                           .sup.4 50 ng/ml recombinant murine MGF was added every 48 hours; specific      activity 10.sup.6 CFU/mg protein                                               .sup.5 N.D. -- not determined.                                           

                                      TABLE XII                                    __________________________________________________________________________     Differential Analysis of CD34.sup.+  DR.sup.-  CD15.sup.-  Cells               following Culture with Various Cytokines                                                  Blasts                                                              Cytokines                                                                             Day %    Pro Myelo                                                                               Meta                                                                               Band                                                                               Seg Baso                                                                               Eos Mono                              __________________________________________________________________________     Post Sort                                                                             0   82   1   1                6       10                                IL-3.sup.1                                                                            7   10   8   16   2       9   50  2   3                                        14  2    4   39   4   3   10  28      10                                       28  3    6   13   3   1   6   61      7                                 FP.sup.2                                                                              7   10   21  52   5       2   7       3                                        14  1    4   17   8   3   20  14      33                                       28       1   24   7   4   36  8       20                                MGF.sup.3                                                                             7   54   39  3                1       3                                        14  30   38  9    1   1       1       20                                       28  1    7   21   18  13  15  1   1   23                                MGF/FP 7   29   22  23   3       4   18      1                                        14  11   22  16   4   2   4   13      28                                       28  1    8   13   12  2   10  2       52                                MGF/IL-3                                                                              7   31   15  48           2   4                                                14  17   14  9    2   4   8   34      12                                       28       8   46   17  2   17  2       8                                 __________________________________________________________________________      Differential cell counts were performed on WrightGiemsa-stained                cytocentrifuge preparations of cells removed from liquid culture.              ≧100 cells per sample were classified. Abbreviations: Pro,              promyelocyte; Myelo, myelocyte; Meta, metamyelocyta; Band, neutrophil ban      form; Seg, segmented neutrophil; Baso, basophil; Eos, eosinophil; Mono,        monocyte.                                                                      .sup.1 500 pg/ml recombinant human IL3, specific activity 3.5 ×          10.sup.2 CFU/ml protein                                                        .sup.2 10 ng/ml recombinant human FP, specific activity 1-2 ×            10.sup.3 CFU/mg protein                                                        .sup.3 50 ng/ml recombinant murine MGF, specific activity 10.sup.6 CFU/mg      protein                                                                  

                  TABLE XIII                                                       ______________________________________                                         Total CFU-GM Production by CD34.sup.+  DR.sup.-  CD15.sup.-                    Cells Cultured in the Presence of Various Cytokines                            CFU-GM/ml culture.sup.1                                                                 Week                                                                  Cytokine   1      2       3     4     6     8                                  ______________________________________                                         Donor 1                                                                        None       8      0       0     0     0     0                                  IL-3.sup.2 132    28      80    N.D..sup.5                                                                           N.D.  128                                GM-CSF.sup.3                                                                              192    112     88    N.D.  128   0                                  IL-3/GM-CSF                                                                               196    104     36    N.D.  128   576                                FP.sup.4   86     112     128   176   N.D.  64                                 MGF.sup.5  290    396     608   448   96    0                                  MGF/FP     376    1,600   14,800                                                                               38,000                                                                               80,000                                                                               0                                  MGF/IL-3   144    348     104   416   2,528 192                                Donor 2                                                                        None       0      0       0     0     0     N.D.                               IL-3       232    196     96    16    64    N.D.                               FP         84     148     288   320   544   N.D.                               MGF        106    152     360   64    128   N.D.                               MGF/FP     114    1,440   10,600                                                                               N.D.  N.D.  N.D.                               MGF/IL-3   62     240     504   32    1,024 N.D.                               Donor 3                                                                        MGF/FP     N.D.   12,448  32,264                                                                               32,264                                                                               1,254 0                                  ______________________________________                                          Total CFUGM = CFUGM/ml culture/(n).sup.n where n = number of previous          demidepopulations.                                                             .sup.1 Cultures were seeded at 5 × 10.sup.3 cells/ml. CFUGM/5            × 10.sup.3 cells in initial population: Donor 1, 150; Donor 2, 227,      Donor 3, 144. Colonies grown in methylcellulose containing 500 pg/ml GMCS      and 1 U human urinary erythropoietin and enumerated after 14 days.             .sup.2 500 pg/ml recombinant human IL3 was added every 48 hours; specific      activity 3.5 × 10.sup.8 CFU/mg protein.                                  .sup.3 250 pg/ml recombinant human GMCSF was added every 48 hours;             specific activity 2 × 10.sup.8 CFU/mg protein.                           .sup.4 10 ng.ml recombinant human FP was added every 48 hours; specific        activity 1-2 × 10.sup.3 CFU/mg protein.                                  .sup.5 ng/ml recombinant murine MGF was added every 48 hours; specific         activity 10.sup.6 CFU/mg protein.                                              .sup.6 N.D. -- not determined.                                           

                  TABLE XIV                                                        ______________________________________                                         Total BFU-E Production by CD34.sup.+  DR.sup.-  CD15.sup.-  Cells              Cultured in the Presence of Various Cytokines                                  BFU-E/ml culture.sup.1                                                                     Week                                                               Cytokine      1            2        3        4                                 ______________________________________                                         Donor 1                                                                        None          0            --       --       --                                IL-3          24           0        0        0                                 GM-CSF        8            0        0        0                                 IL-3/GM-CSF   22           4        0        0                                 FP            20           4        0        0                                 MGF           8            40       0        0                                 MGF/FP        98           0        0        0                                 MGF/IL-3      238          4        0        0                                 Donor 2                                                                        C             0            --       --       --                                IL-3          40           28       0        0                                 FP            132          68       56       16                                MGF           6            0        0        0                                 MGF/FP        662          100      200      0                                 MGF/IL-3      1,062        272      40       0                                 ______________________________________                                          Total BFUE  BFUE/ml culture/(N).sup.n where n = number of previous             demidepopulations.                                                             .sup.1 Cultures were seeded at 5 × 10.sup.3 cells/ml. Each point         represents the mean of two separate experiments. Mean BFUE/5 ×           10.sup.3 cells in initial population: = Donor 1, 173; Donor 2, 154.            Colonies grown in methylcellulose containing 500 pg/ml GMCSF and 1 U huma      urinary erythropoietin and enumerated at 12 days.                              .sup.2 500 pg/ml recombinant human IL3 added every 48 hours; specific          activity 3.5 × 10.sup.6 CFU/mg protein.                                  .sup.3 250 pg/ml recombinant human GMCSF added every 48 hours; specific        activity 2 × 10.sup.8 CFU/mg protein.                                    .sup.4 10 ng/ml recombinant human FP[ added every 48 hours; specific           activity 1-2 × 10.sup.8 CFU/mg protein.                                  .sup.5 50 ng/ml recombinant murine MGF added every 48 hours; specific          activity 10.sup.8 CFU/mg protein.                                        

                  TABLE XV                                                         ______________________________________                                         Total CFU-MK Production by CD34.sup.+  DR.sup.-  CD15.sup.-                    Cells Cultured in the Presence of Various Cytokines                            CFU-MK/ml culture.sup.1                                                                 Week                                                                  Cytokine   2     3       4    5     8     10                                   ______________________________________                                         Donor 1                                                                        None       0     0       0    0     0     0                                    IL-3.sup.2 14    74      100  118   48    N.D..sup.6                           GM-CSF.sup.3                                                                              12    40      20   48    32    0                                    IL-3/GM-CSF                                                                               20    80      96   120   N.D.  N.D.                                 FP.sup.4   28    120     184  118   96    64                                   MGF.sup.5  6     12      36   20    0     0                                    MGF/FP     40    120     120  120   N.D.  0                                    MGF/IL-3   26    90      208  220   128   64                                   Donor 2                                                                        None       8     0       0    0     0     0                                    IL-3       26    100     140  140   64    64                                   GM-CSF     24    40      60   80    32    0                                    IL-3/GM-CSF                                                                               40    120     160  200   64    64                                   FP         56    120     200  200   96    64                                   MGF        10    3       60   60    0     0                                    MGF/FP     56    200     200  200   40    0                                    MGF/IL-3   34    120     240  260   160   192                                  ______________________________________                                          Total CFUMK  CFUMK/ml culture/(N).sup.n  where n = number of previous          demidepopulations.                                                             .sup.1 Cultures were seeded at 5 × 10.sup.3 cells/ml. Each point         represents the mean of two separate experiments. Mean CFUMK/5 ×          10.sup.3 cells in initial populations = 0. Colonies cultured in fibrin         clot containing 1 ng IL3 and enumerated at 15 days.                            .sup.2 1 ng/ml recombinant human IL3 was added every 48 hours; specific        activity 3.5 × 10.sup.3 CFU/mg protein.                                  .sup.3 200 pg/ml recombinant human GMCSF was added every 48 hours;             specific activity 2 × 10.sup.8 CFU/mg protein.                           .sup.4 10 ng/ml recombinant human FP was added every 48 hours; specific        activity 1-2 × 10.sup.8 CFU/mg protein.                                  .sup.5 100 ng/ml recombinant murine MGF was added every 48 hours; specifi      activity 10.sup.6 CFU/mg protein.                                              .sup.6 Not determined.                                                   

    ______________________________________                                                  Week                                                                           1     2       3      4     6    8                                     Cytokine   % plating Efficiency.sup.1                                          ______________________________________                                         None       N.D..sup.6                                                                             --      --   --    --   --                                  IL-3.sup.2 0.86    0.072   0.023                                                                               0.003 0.005                                                                               0.009                               GM-CSF.sup.3                                                                              1.67    0.105   0.020                                                                               N.D.  0.005                                                                               0.000                               IL-3/GM-CSF                                                                               0.96    0.044   0.005                                                                               N.D.  0.006                                                                               0.028                               FP.sup.4   0.42    0.039   0.019                                                                               0.010 0.015                                                                               0.002                               MGF.sup.5  2.58    0.493   0.580                                                                               0.065 0.031                                                                               0.000                               MGF/FP     0.65    0.127   0.056                                                                               0.029 0.015                                                                               0.000                               MGF/IL-3   2.10    0.173   0.041                                                                               0.008 0.019                                                                               0.002                               ______________________________________                                          .sup.1 % Plating Efficiency = colonies enumerated/cells cultured ×       100%. Cells at each timepoint were counted and cultured in methylcellulos      containing 500 pg GMCSF and 1 U human urinary erythropoietin or in fibrin      clot containing 1 ng IL3 and enumerated at 14 days. Each point represents      the mean of two to four separate experiments. Mean cloning efficiency of       initial (day 0) population: 4.54%                                              .sup.2 500 pg/ml recombinant human IL3 was added every 48 hours; specific      activity 3.5 × 10.sup.8 CFU/mg protein                                   .sup.3 200 pg/ml recombinant human GMCSF was added every 48 hours;             specific activity 2 × 10.sup.8 CFU/mg protein.                           .sup.4 10 ng/ml recombinant human FP was added every 48 hours; specific        activity 1-2 × 10.sup.8 CFU/mg protein.                                  .sup.5 100 ng/ml recombinant murine MGF was added every 48 hours; specifi      activity 10.sup.8 CFU/mg protein.                                              .sup.6 N.D. -- Not determined.                                           

EXAMPLE 4

Serum-free long-term suspension human bone marrow culture system. Serum-free media was prepared as previously outlined by Ponting et al. (19). Both serum-free and serum-containing cultures were initiated with CD34⁺ DR⁻ CD15⁻ cells and supplemented every 48 hours with KL and a GM-CSF/IL-3 fusion molecule (FP).

As can be seen in Table XVII, cultures maintained in serum-free media were characterized by far less total cell production than has been observed in comparable serum containing culture. Over the 6 weeks of observation, these LTBMCs exhibited a mere 24-fold increase in total cell numbers, yet were characterized by a 6-fold increase in CFU-GM and a 1.8-fold increase in HPP-CFC. Remarkably, however, the progenitor cell cloning efficiency in serum-free cultures was 1.4% after 28 days of LTBMC (Table XVII) in comparison to a cloning efficiency of 0.03% in comparable serum-containing cultures. These studies suggest that the serum-free culture system is preferred for expanding progenitor cell numbers at the expense of impairing the production of more differentiated cells.

                  TABLE XVII*                                                      ______________________________________                                                          Progenitor Cells                                              Day in Culture                                                                            Cell No. × 10.sup.3                                                                  CFU-GM     HPP-CFC                                      ______________________________________                                          0         10          375        40                                           14         30          744         9                                           28         70          1,050      21                                           42         140         140        42                                           ______________________________________                                          *CD34.sup.+  DR.sup.-  CD15.sup.-  cells were susp]ended in serumfree          medium and supplemented with 100 ng/ml of KL and 10 ng/ml of FP every 48       hours.                                                                   

References:

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What is claimed is:
 1. A method for growing human hematopoietic stem cells in a liquid culture medium, the method comprising:adding said human hematopoietic stem cells to a liquid culture medium essentially free of stromal cells, comprising the cytokine mast cell growth factor (MGF) maintained at a concentration of at least 10 ng/ml, in an amount effective to provide for an expansion in the cell number in said population from at least about 100 fold and not more than about 200 fold within a period of 26 days; and growing the population of said human hematopoietic stem cells in said medium.
 2. A method according to claim 1, wherein said human hematopoietic stem cells are characterized as being CD34⁺ DR⁻ CD15⁻.
 3. A method for growing human hematopoietic stem cells in a liquid culture medium the method comprising:adding said human hematopoietic stem cells to a liquid culture medium essentially free of stromal cells, comprising the cytokine mast cell growth factor (MGF) maintained at a concentration of at least 10 ng/ml, wherein said medium further comprises at least one cytokine selected from the group consisting of interleukin 3 (IL-3) maintained at a concentration from about 500 pg/ml; granulocyte macrophage colony stimulating factor (GM-CSF) maintained at a concentration from about 100 pg/ml and IL-3/GM-CSF fusion protein maintained at a concentration from about 1 ng/ml; in an amount effective to provide for an expansion in the cell number in said population from at least about 100 fold and not more than about 20,000 fold within a period of 26 days; and growing the population of said human hematopoietic stem cells in said medium.
 4. A method according to claim 3, wherein said cytokines are added to said culture medium every 48 hours.
 5. A method for growing human hematopoietic stem cells in a liquid culture medium, wherein said human hematopoietic stem cells are characterized as being CD34⁺ DR⁻ CD15⁻, the method comprising:adding said human hematopoietic stem cells to a medium essentially free of stromal cells, comprising the cytokine mast cell growth factor (MGF) maintained at a concentration of at least about 10 ng/ml, and at least one cytokine selected from the group consisting of interleukin 3 (IL-3) maintained at a concentration from about 0.5 ng/ml; granulocyte macrophage colony stimulating factor (GM-CSF) maintained at a concentration from about 0.2 ng/ml and IL-3/GM-CSF fusion protein maintained at a concentration from about 10 ng/ml; in an amount effective to provide for an expansion in the cell number in said population from at least about 100 fold and not more than about 2,000 fold within a period of 26 days; growing the population of said human hematopoietic stem cells in said medium for at least about 26 days. 